This invention relates generally to temperature sensing devices which are suitable for repeated immersions into molten metal. In particular this inventions relates to improvements to a molten metal temperature sensing device which includes a high temperature protection tube of a fiberous refractory material.
As shown by Kraus, U.S. Pat. Nos. 3,816,183, and Falk, No. 4,521,639, it is known to surround a temperature sensing device with a cylindrical sleeve of refractory material for achieving repeated immersions into a molten metal bath. The co-pending application referred to above shows a refractory sleeve having a generally cylindrical bore initiating at one end and terminating at an inwardly projecting shoulder and a tapered or truncated cone shape cylindrical bore which extends from the shoulder through the opposite end of the sleeve.
The construction of the repeating device includes a support tube surrounding a thermocouple unit which is inserted into the cylindrical bore of the refractory sleeve. A projecting portion of the thermocouple unit extends through the cone shaped bore and away from the end of the sleeve by a predetermined distance. The refractory sleeve is secured to the support tube by filling the end of the sleeve with a refractory cement.
The invention described herein is an improvement over the structures shown and described in the previous mentioned patents and pending application so as to further increase the number of immersions that the sensing device may be utilized prior to failure.